The invention relates to an incandescent lamp for a motor vehicle headlamp in accordance with the preamble of patent claim 1.
Such an incandescent lamp is disclosed, for example, in European laid-open specification EP 0 791 779. This publication describes a motor vehicle headlamp having a double-filament halogen incandescent lamp that has an axially symmetrical lamp vessel with an incandescent filament aligned axially therein, and an incandescent filament aligned transversely, as well as a shading device for the axial filament.
It is the object of the invention to provide an incandescent lamp having an improved frame design. The aim, in particular, is to ensure that the light emission of the incandescent filaments is obstructed as little as possible by their supply leads, and that shading effects in the principal light emission direction of the incandescent filaments through the supply leads are reduced.
This object is achieved according to the invention by the features of patent claim 1. Particularly advantageous embodiments of the invention are described in the dependent claims.
In the case of the incandescent lamp according to the invention, the frame that serves to hold and supply power to the incandescent filaments is designed in such a way that at least one power supply wire, preferably the power supply wire serving to hold the shading device, has a section that projects out of the common plane of the power supply wires and is guided past the transversely aligned incandescent filament and is shaped in such a way that it is arranged outside the principal light emission direction of the second incandescent filament. By principal light emission direction is meant the directions running perpendicular to the longitudinal axis of the transversely aligned incandescent filament. Instead of this, the above-named power supply wire is guided past the transversely aligned incandescent filament such that light beams that this incandescent filament emits perpendicular to its longitudinal axis cannot strike the above-named power supply wire. For this purpose, this power supply wire has a section that projects out of the common plane of the power supply wires and is guided past the transversely aligned incandescent filament, and is shaped or arranged in such a way that it is not struck by light beams that this incandescent filament emits perpendicular to its longitudinal axis. If the motor vehicle headlamp predominantly uses only the downwardly emitted light fraction of the transversely aligned incandescent filament, it is sufficient that only the power supply wire supporting the shading device is guided past the transversely aligned incandescent filament, in order distinctly to reduce the shading effects owing to the frame, and appreciably to increase the useful fraction of the light emitted by the transverse filament. If the motor vehicle headlamp makes predominant use only of the upwardly emitted light fraction of the transversely aligned incandescent filament, it is sufficient that only the power supply wire connected to the axially aligned incandescent filamentxe2x80x94that is to say the incandescent filament aligned parallel to the lamp vessel axisxe2x80x94is guided past the transversely aligned incandescent filament, in order distinctly to reduce the shading effects owing to the frame, and appreciably to increase the useful fraction of the light emitted by the transverse filament. The shading effects can be diminished most strongly when both abovementioned power supply wires are guided past the transverse filament.
The frame design according to the invention is also distinguished, furthermore, by a particularly simple construction. The three power supply wires are fixed in a common plane perpendicular to the longitudinal axis of the incandescent filament aligned transversely with reference to the lamp vessel axis. The purpose of holding and making electrical contact with the transversely aligned incandescent filament is advantageously served by the section, projecting out of the common plane, of the power supply wire supporting the shading device, and by a bent end, projecting out of the common plane, of the first power supply wire. The ends of the transversely aligned incandescent filament need not therefore be bent in order to produce a connection with its power supply wires. The resistance of the lamp or the filament holder to vibration is thereby increased.
The section, projecting out of the common plane of the power supply wires, of the power supply wire supporting the shading device is advantageously of substantially trapezoidal construction, and the end of this section is advantageously arranged obliquely relative to the lamp vessel axis and welded to the shading device. As a result, only three bending points are required in order for the power supply wire supporting the shading device to be guided past the transversely aligned incandescent filament.
The shape of the shading device for the axial filament has likewise been improved. On its side facing the axially aligned incandescent filament, it has an elevation in order to be able to weld the end of this incandescent filament more easily to the shading device. Moreover, the shading device has a slightly curved shader nose that extends into the interspace between the two incandescent filaments. The width of the shader nose advantageously corresponds to the length of the light-emitting part of the transverse filament, in order largely to avoid mutual influencing of the light emission of the two incandescent filaments. The side of the shading device averted from the axial filament is advantageously provided with one or more projections running obliquely relative to the lamp vessel axis, in order to ensure a reliable welded joint between the shading device and the power supply wire supporting it.